The present invention relates to a support pad for the outdoor component of a split air conditioning (AC) system and installation method that not only raises the AC outside unit off the ground at least 4 inches as required by most building codes but that also secures that unit to prevent theft and further to secure the unit in high wind situations, such as hurricanes.
Typically, an AC pad is constructed of poured concrete formed in situ. This may be convenient in some cases, such as when other concrete work is being performed on site. However, an installer would find mixing or purchasing concrete specifically for this small application to be impractical, time consuming, or expensive.
As an alternative, prefabricated plastic and concrete pads are available for transport and placement on site. Available plastic pads, however, are typically lightweight and do not provide the required wind resistance once a AC unit is mounted on the pad. Similarly, preformed solid concrete pads are heavy and difficult to handle. Concrete pads with lightweight foam interiors such as the “The Hurricane Pad™” manufactured by DiversiTech (Duluth, Ga.) are somewhat fragile. As a result, these foam interior pads can be damaged, if dropped. In other cases, foam-cored pads are too light to secure an air conditioner in high winds.
A hurricane-wind rated AC pad must be able to keep the AC outdoor unit in place during high winds and also prevent the AC unit from toppling over or moving. The minimum necessary weight of the pad is dependent on the size and weight of the AC unit and the wind speed. Hurricane resistant AC pads must survive wind speeds up to 180 mph, with the actual required wind speed dependent on the location.
For example, Table 1 below provides the minimum weight necessary for a 36 inch×36 inch pad to secure various sizes and weights of AC units. The wind load is calculated from the methods presented in American Society of Civil Engineers (ASCE) Standard 7-16. The AC unit is an assumed to be a rigid structure and on flat ground in a moderately open area. The dimensions and weights of the AC units listed in Table 1 are based on actual commercially available outdoor units used in current split AC units and represent an example of the range of currently available actual AC outdoor units that could be mounted to such pads. Modern high efficiency AC of units have become much taller, to allow greater heat exchanger area on the same footprint, and this has exacerbated the wind-driven tipping issue. For example, in Table 1, the Required Pad Weight has increased from 130 pounds for a 24×24×30-inch-high outdoor unit to 540 pounds for a 32×32×50 inch high outdoor unit. Building codes also require a minimum of a 2 inch border around the perimeter of any AC outdoor unit, so that a 32 inch base is the largest AC that can be placed on a 36 inch pad. Another common pad size is 42×42 inches., and by following the calculation procedures outlined in ASCE Standard 7-16, one skilled in the art could calculate the required weight to prevent tipping for an pad size and air conditioner geometry.
TABLE 1Required AC unit pad weight to resist tipping.AC Unit DimensionsRequired Pad WeightWidthLengthHeightWeight150 mph 180 mph (in)(in)(in)(lb)Wind (lb)Wind (lb)242430100591302424351209719326263012053129262635140951992828301404612828283516093205 282840190141286303030160391273030351908120130304022013429030304524020840632323522069197323240250128294323245280198409323250310281540Table 1 makes clear that a concrete pad would need to be quite heavy to prevent tipping due to the moment caused by wind, making it very difficult to carry one into place at the installation site.
One known approach proposed the use of a hollow pad with a hollow interior chamber filled with sand, other granular materials, or water so as to achieve the necessary weight required to prevent the pad from tipping in the case of hurricane winds. With water, the pad was not intended to be completely filled so that in colder climates, the expansion of frozen water would not damage the pad. Even if such a pad were completely filled with water and a height increased to 6 inches, for certain tall outdoor AC unit geometries, the water alone would not provide sufficient weight to keep the pad in place in the highest possible winds, such as 180 mph winds. Another way to secure the pad such as the use of higher density materials inside the hollow pad, such as the use of sand, are known in the art. At least one central support has also been proposed to prevent sagging, but that would limit the ability of a granular material like sand to completely fill the hollow core and reduce the fill volume and therefor the weight of the filled pad. If the central support is large, it can significantly reduce the volume of fill material available for weighing the pad down.
One of the objects of our invention is to provide an easily transportable, lightweight, rugged, and low-cost AC pad and installation method that, once located and leveled on site, can be secured to prevent theft and tipping, even in high wind loads. Our novel AC pad can be configured as a hollow plastic shell that can be rotationally molded to reduce cost and minimize weight. If the pad is formed by conventional rotational molding, the molded pad will typically be formed from one of a variety of thermoformed plastics. The currently preferred embodiment uses a linear low-density polyethylene (LLDPE)) to form a rigid structure with uniform wall thickness. However, any thermoform-capable material such as low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), cross linked polyethylene (XLPE) nylon, polypropylene, and polyvinyl chloride (PVC) are acceptable alternatives. While the currently preferred material wall thickness for the pad is 0.2 inches throughout the pad, alternative embodiments can use material thicknesses from 0.1 inches to 0.75 inches with, if desired to reduce costs, non-uniform wall thickness by using well known shielding on the rotational mold to adjust cooling times and thereby obtain non-uniform wall thicknesses. For example, the side-walls could be 0.1 inches, the top AC bearing surface 0.5 inches and the bottom soil facing surface 0.2 inches. Of course, support structures can be used to ensure sufficient support without the need to thicken an entire surface. As pointed out herein, these support structures can also serve as adjustable securing locations for tie-down straps.
Once located and leveled, the empty shell that contains a gelling formulation of known composition according to our invention can be filled with water and sealed, and securing straps installed in the pad before the AC outdoor unit is located on the pad can be attached to the AC unit to secure the unit to the pad. The filling water is converted to a solidus or gel state due to the gelling formulation already present inside the empty pad structure. The gel/solidus conversion will be used to prevent weight loss, even if the leak-tight seal is compromised. Additionally, if a super absorbent polymer (SAP), such as sodium polyacrylate, sodium polycarbonate, polyacrylamide copolymers, ethylene maleic anhydride, carboxymethylcellulose, polyvinyl alcohol copolymers, or polyethylene oxide, is used in the gelling compound formulation, then the resulting mixture will not expand upon freezing, thereby allowing the pad to be completely filled with water, with the added benefit of avoiding the need for an expansion void space. Filling the interior volume completely with the gelled water also allows the filling mixture to provide support to the pad, thereby serving to prevent deformation and avoiding the need for any internal structure, since the required support to prevent deflection can be supplied by the filled interior volume of the entire pad. This novel approach provides a uniform support and avoids any localized deflections in regions distant from a central support if a central support is used.
In the event the AC pad according to our invention were increased to heights above 4 inches and arguably, when filled, may still not be considered to provide sufficient weight to prevent tipping in the highest wind conditions, anchors can be screwed or driven into the soil in order to add additional tipping resistance.
Our novel AC pad will connect to the outdoor AC unit through easily adjustable securing straps that, once installed though the bottom of the pad, cannot be removed without first lifting the air conditioning unit and pad. Of course, lifting the pad is much more difficult after the pad is secured to the underlying soil and filled with water. The securing straps are installed through slots open to the bottom of the AC pad and connected directly to the AC unit. The straps are able to rotate and move to accommodate various sizes and shapes of AC units. Additionally, extra slots and slots at various slot angles can be made available for use without departing from the scope of our invention.
In addition, theft of the AC unit will be deterred because of the combined weight of the AC pad and the AC outdoor unit, and if used, the lifting strength of the anchors driven into the ground. Moreover, our invention contemplates that the AC outdoor unit can be connected to the AC pad with known types of anti-theft fasteners, such as machine or sheet metal screws with unique heads that can only be unscrewed with a special tool. An anti-theft cable can also be installed. Similar to the securing straps, the anti-theft cable connects to the pad using one of the unused slots and is installed though the bottom of the pad (before the pad is secured in place). Like the securing straps, the cable cannot be removed without first lifting the pad. The other end of the anti-theft strap is connected to some portion of the AC outdoor unit using anti-theft fasteners, similar to those used for the straps.